I am the owner of a Honda motorcycle [CBX1000] who lives in Hiroshima City, Japan. I am posting about FCR carburetor and CBX1000 customization. I also post about things other than cars and motorcycles. We will post information that will make bikers around the world happy.
FCR Tuning – Acceleration Pump Discharge Timing Adjustment – Finalized as is – 2023-06-20
Tuning the Acceleration Pump Start Position.
Recently, I’ve been curious about it, so I started with a test ride. As a result, I ended up making adjustments and then returning it to its original setting. I’ve been deliberately rough with throttle work. However, I made sure to accelerate smoothly, paying careful attention to the shift position and how the speed builds up during the test ride. I'll now share my thoughts and impressions from the test ride.
I adjusted the acceleration pump, but in the end, I reverted it to the original setting. There didn’t seem to be much change. It might be due to my throttle work. If the acceleration pump discharge timing is too early, there can be cases where the fuel hits the throttle valve directly. While there might not be any major negative effects, I’m psychologically averse to making the discharge timing too early.
Regarding the Tuning of the Acceleration Pump
Tuning the FCR Acceleration Pump
The FCR acceleration pump allows you to change the discharge timing. You can also adjust the total discharge volume by tweaking the acceleration pump diaphragm. By the way, the total volume of the acceleration pump refers to the duration of the discharge. It doesn't change the intensity or force of the discharge, although it might slightly affect it. Think of it as adjusting the discharge duration. The total amount is the time it takes from when the fuel starts to discharge until it stops.
In the FCR, you can only adjust how much throttle opening triggers the discharge and how long it lasts. Another adjustment method is to fix the push rod and physically turn off the acceleration pump. When you suddenly open the throttle, the engine sucks in a lot of air, which causes the carburetor to exhibit lean symptoms. The acceleration pump helps to suppress these lean symptoms at that moment. The FCR, including the effect of the acceleration pump, provides a sharp acceleration feeling. The acceleration pump is what creates that sharp acceleration.
Please make sure to adjust the acceleration pump until you are satisfied with it.
Note: In some cases, turning off the acceleration pump might result in even sharper acceleration.
Single-Carburetor Motorcycles like the SR400 and the Acceleration Pump
Acceleration Pumps for Single-Carburetor Motorcycles like the SR400
The total discharge volume of the acceleration pump is the same for both single-carburetor motorcycles like the SR400 and four-cylinder engines. Using the same acceleration pump discharge volume for single-cylinder and four-cylinder engines can present issues. I believe that the standard acceleration pump diaphragm is appropriate for four-cylinder engines. For single-carburetor setups like the SR400, it is common to switch to a diaphragm with a lower discharge volume, such as the one used for the KX400. The KX400 has a lower discharge volume compared to the KX250.
The SR400 can be equipped with FCR carburetors at a lower cost compared to those for four-cylinder or six-cylinder engines. Considering the TMR or TMR-MJN is also an option. Carburetors are outdated devices, and among them, I believe the latest TMR series offers the best performance. Whether to use the TMR or TMR-MJN depends on personal preference. The TMR-MJN incorporates a jet needle developed by Yoshimura and also has differences in appearance.
FCR Beginners – Tuning is a Repeated AB Test
Regarding the Tuning of the Acceleration Pump Discharge Timing
In this case, I adjusted the discharge timing as follows: 1.00mm → 0.60mm → 1.00mm and returned it to the original setting.
There are two key points I want to convey about FCR tuning:
1. Make Comparisons 2. Keep a Record of the History Without making comparisons and keeping records, tuning cannot be considered effective. Even a simple comparison, such as whether things have improved or worsened compared to the previous setting, is sufficient. Quantifying these changes is also an important indicator. The feeling you get when riding the motorcycle is crucial. It’s necessary to judge which setting is better before and after the tuning.
It’s essential to keep records, even if they are minimal. Without a record of past work, you may end up repeating the same tuning adjustments multiple times in the same area. Comparisons and records are things even beginners can start doing immediately. Make it a habit.
FCR Tuning – Acceleration Pump Discharge Timing Adjustment – Finalized as is – 2023-06-20【summary】
Regarding This Tuning Session
In this tuning session, I experimented with changing the acceleration pump discharge timing. The result was that I ended up reverting to the original setting. One thing became clear: changing the acceleration pump discharge timing did not make a difference with my throttle operation. I found that there was no noticeable change. Understanding this is important.
For the time being, I will not be tuning the discharge timing to 0.60mm again. While it’s case-by-case and there’s no definitive answer, I don’t plan to make this change for the foreseeable future. I might use the 0.6mm setting in a few years or if there is a major change in the tuning specifications.
This was a report on the acceleration pump tuning. Some of you might experience days when you can't ride your motorcycle due to rain. Use that time to work on maintenance, purchase parts, or prepare for future projects. Let’s continue to enjoy motorcycling despite the weather.
See you again!
CBX1000 – Photo Gallery
I’ve extracted photos related to the acceleration pump.
